1. Field of the Invention
The present invention relates to an optical device integrating an optical modulator for modulating color light in accordance with image information and a color combining optical device for combining the color light modulated by the optical modulator, an optical unit provided with the optical device and a projector provided with the optical unit.
2. Description of Related Art
Conventionally, so-called three-plate projector in which a light beam irradiated by a light source is separated into three color-lights of red, green and blue which are modulated by three liquid crystal panels for respective color-lights in accordance with image information and are combined by a cross dichroic prism after being modulated, and a color image is enlarged and projected through a projection lens, is known.
Since the respective liquid crystal panels of such projector have to be located at back-focus position of the projection lens, an optical device having position-adjusted liquid crystal panel directly fixed on the light-incident side of the cross dichroic prism to be integrated has been conventionally used.
In attaching the liquid crystal panel and the cross dichroic prism of the integrated optical device, as shown in Japanese Patent Laid-Open Publication No. 2000-221588, a hole is formed on four corners of a holding frame accommodating the liquid crystal panel and pins are inserted into the holes to attach the liquid crystal panel on the light-incident side of the cross dichroic prism, or alternatively, as shown in Japanese Patent Laid-Open Publication No. Hei 10-10994, a wedge-shaped spacer is interposed between the holding frame and the cross dichroic prism to fix the liquid crystal panel on the light-incident side of the cross dichroic prism.
Such optical device has a polarization plate for aligning polarization direction of the respective color-lights modulated by the liquid crystal panel between the liquid crystal panel and the light-incident side of the cross dichroic prism, the polarization plate being ordinarily attached and fixed on the light-incident side of the cross dichroic prism.
In the optical device integrating the liquid crystal panel, the cross dichroic prism and the polarization plate etc., the liquid crystal panel and the polarization plate heated by irradiating light beam from the light source are forcibly cooled through a gap formed between the liquid crystal panel and the polarization plate by the pin or the spacer, where cooling air is introduced into the gap using an air-cooling fan etc.
However, since the size of the optical device itself is reduced in accordance with recent size reduction and increase in luminance of projector, which results in small gap between the liquid crystal panel and the polarization plate, it is difficult for the cooling air to enter into the gap, thereby lowering cooling efficiency and deteriorating liquid crystal panel and polarization plate.
The cooling efficiency can be improved by increasing the amount of the cooling air flowing through the gap, which, however, increases the noise of the cooling fan. Further, in order to increase the amount of the cooling air, the size of the cooling fan has to be increased, which requires greater size of the projector itself to hinder size reduction of the projector.
Accordingly, an arrangement for the optical device has been proposed, where a base made of material having excellent heat-conductivity such as metal is attached to a side intersecting the light-incident side of the cross dichroic prism, the polarization plate is bonded on the base and the liquid crystal panel is fixed on the polarization plate through a position-adjusting spacer by an adhesive having excellent heat-conductivity.
According to the above optical device, the heat generated on the polarization plate and the liquid crystal panel can be transferred to the base and the base can be forcibly cooled by a fan etc., overheat of the polarization plate and the liquid crystal panel can be prevented.
However, according to the optical device where the heat is transferred to the base, the heat generated on the polarization plate and the liquid crystal panel may not be entirely transferred to the base and the heat may conduct from high-temperature polarization plate to relatively low-temperature liquid crystal panel according to the polarization plate and the liquid crystal panel, so that the temperature of all the polarization plate and the liquid crystal panel may not be securely cooled and sufficient cooling efficiency may not be obtained.
Further, since sufficient cooling efficiency cannot be obtained, size reduction and enhancement in luminance of the projector may be hindered.